Kouyate joined Tomkins at West Ham United in 2014 and they both played together before the latter left for south London in July 2016.
After signing a four-year deal with the Eagles this summer, the 29-year-old midfielder will play alongside his former teammate and compatriot Pape Souare in Roy Hodgson's team this season.
“He is a good guy. I loved the fella at West Ham and still do," Tomkins told Football London.
"He is a really happy guy, not too jokey, but he has that character where he is always smiling.
"He is a good player as well. It was a surprise for me that West Ham let him go but it is to our gain for sure.
“He has got so much energy. He breaks into the box and can score headers, which maybe is something we have not got.
"I think he is something we needed. He can get up and down the pitch very well. Has a lot of energy and he is not scared to put his foot in.”